For some strange reason, I was having issues with transferring select files using Unison from my Linux machine to my Mac after I upgraded from Ubuntu 18.04 to 20.04. My Unison version was the same on both, and nearly all files transferred as before, but I kept getting errors like:

failed: files/dining.doc

on a subset of files. (The path and filenames above are fake and illustrative.) It turned out the problem was there was a hidden file in files named ._dining.doc that was causing the failure. Once I deleted these hidden files, everything worked!

(Last updated August 24, 2021.)